1. Field of the Invention
The present invention relates generally to a tubing conveyed perforating gun system of the type used to perforate a well bore for the production of well bore fluids, and, specifically, to such a system with internal components designed to decrease firing debris and to allow reverse washing of fill encountered in the well bore, without tripping the system out of the well.
2. Description of the Prior Art
As oil and gas wells are being drilled, the integrity of the borehole is preserved by cementing a casing or liner in place in the borehole. The casing or liner is a metal cylindrical conduit which must be punctured or perforated over the desired production interval in order to produce well bore fluids once drilling is complete. A perforating gun which utilizes some form of fired projectile and an explosive charge is used to perforate the casing or liner to begin production from the well.
Prior perforating gun techniques have either utilized tools which were run on a wireline or cable or have utilized tubing conveyed devices which were run on a tubing string to a desired depth in a well bore. Tubing conveyed devices have certain advantages over wireline methods. For example, tubing conveyed devices allow safe, immediate release of formation pressure at maximum pressure differentials into the tubing string. With tubing conveyed perforating systems, the tubing can be run into position, a packer set to seal off the well bore, and the surface wellhead equipment can be installed. The packer setting can be checked by circulating fluid under pressure through the well annulus or through the well tubing string. Once the surface work is completed and tested for safety, the perforating gun can be fired to bring in the well. Tubing Conveyed Perforating (TCP) systems provide rig time savings, higher shot density, greater gun length and the ability to perforate "under balanced" so that perforations are cleansed through formation fluid backflow. Since perforating guns can be run below the production tubing they enable the well to be perforated and completed, i.e., put into production, in one operation.
Occasionally, sand fill has infiltrated into the well and causes problems with gravel packing or other well bore operations. It is thus desirable to provide an apparatus having the capability of reverse circulating the fill out of the well. Obviously, it is desirable to accomplish the reverse circulation of the fill out of the well without having to pull the work string, gravel packing and/or perforating apparatus.
In wells utilizing a sump packer below the zone to be perforated, it is necessary for the perforating string to have its lower end sealingly engaged with a bore of the sump packer prior to performing the desired well bore operation. With the prior art systems, if sand fill was encountered on top of the sump packer, it was generally necessary to trip the perforating apparatus and its associated tool string out of the well. A work string was then run into the well to reverse circulate the sand fill away from the sump packer. The work string was then required to be tripped out of the well so that the perforating tool string could again be run into the well. Often times, as many as three trips in and out of the well were required before the entire operation could be accomplished.
The present invention has as one object to provide a tubing conveyed perforating apparatus with means for reducing the accumulation of firing debris within the well bore at the conclusion of the firing operation.
Another object of the invention is to provide such an apparatus which allows for the reverse circulation of sand fill encountered within the well bore, such as sand fill encountered directly on top of a sump packer located within the well bore.
Another object of the invention is to provide a tubing conveyed perforating apparatus which allows the plug in a sump packer to be placed and released, perforation of the well casing, reverse circulation of fill and/or debris from the top of the sump packer, and subsequent retrieval of the plug from the sump packer.
Another object of the invention is to provide such an apparatus which is relatively simple in design and economical to manufacture.